Stretch-draw metal forming

ABSTRACT

A stretch bending or dieing mechanism including a drawing die press having a work tensioning or stretching apparatus at opposite ends of a lower horizontally oriented stationary die. Prior to or in timed relation with the movement of the movable die to form the sheet having its opposite ends secured in sheet clamping units of the apparatus, fluid pressure actuated motors which support the sheet clamping units are actuated to lower the units and wrap the sheet partly around the lower die. Simultaneously the units are moved in a predetermined path away from the lower die to tension or stretch the sheet, as desired, preferably by cam means which may be stationary or adjustable. Movement of the sheet clamping units in the directions away from the lower die is resisted by the tension in the work sheet during the forming operation. At other times the positions of the units relative to the die may be controlled by cam means and/or double acting reciprocating type fluid pressure actuated motors.

United States Patent 1191 MacKenzie 1451 Sept. 30, 1975 i 1 STRETCH-DRAW METAL FORMING Robert A. MacKenzie, 8351 Lucerne Dr. Chagrin Falls. Ohio 44022 [22] Filed: Jan. 18, 1974 [21] Appl. No.: 434,661

[76] Inventor:

Primary Etaminer-Richard J. Herbst Assistant E.\'aminerE. M. Combs Attorney, Agent, or FirmWatts, Hoffmann, Fisher & Heinke [57 1 ABSTRACT A stretch bending or dieing mechanism including a drawing die press having a work tensioning or stretching apparatus at opposite ends of a lower horizontally oriented stationary die. Prior to or in timed relation with the movement of the movable die to form the sheet having its opposite ends secured in sheet Clamping units of the apparatus, fluid pressure actuated motors which support the sheet clamping units are actuated to lower the units and wrap the sheet partly around the lower die. Simultaneously the units are moved in a predetermined path away from the lower die to tension or stretch the sheet, as desired, preferably by cam means which may be stationary or adjustable.

Movement of the sheet clamping units in the directions away from the lower die is resisted by the tension in the work sheet during the forming operation. At other times the positions of the units relative to the die may be controlled by cam means and/or double acting reciprocating type fluid pressure actuated motors.

22 Claims, 19 Drawing Figures US. Patent Sept. 30,1975 Sheet10f9 3,908,428

FIG.I

US. Patent Sept. 30,1975 Sheet 2 of9 3,908,428

N QE

US. Patent Sept. 30,1975 Sheet 3 of9 3,908,428

US. Patent Sept. 30,1975 Sheet4of9 3,908,428

US. Patent sfipt. 30,1975 shw 5 of9 3,908,428

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US. Patent Sept. 30,1975 Sheet 6 of9 3,908,428

2 FIG. I2

US. Patent Sept. 30,1975 Sheet 7 of9 3,908,428

US. Patent Sept. 30,1975 Sheet 8 of 9 3,908,428

FIG. I?

US. Patent Sept. 30,1975 Sheet 9 of9 3,908,428

FIG. l8

FIG. l9

. 1 STRETCH-DRAW METAL FORMING FIELD OF THE INVENTION.

This invention relates to metal forming by use of indi-.

vidual non-deforming work-gripping, clamps movable relative to a coacting tool or die sometimes referred to as stretch bending.

PRIOR ART Metal forming mechanism using individual non- SUMMARY OF THE INVENTION The present invention provides novel and improved metal forming apparatus comprising work gripping clamps at opposite ends of a stationary die movable to tension or stretch and wrap the work sheet partly about the die wherein the paths of movements of'the work clamps on their return to starting position'are different from those followed on their forward or working strokes.

The above and other features and advantages of this invention will become more apparent as the invention becomes better understood from the detailed description of a preferred embodiment when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a front elevational view of av drawing die press embodying the present invention, with'the parts in position to receive a metal sheet 'to be formed;

FIG. 14 is a view similar to FIG. 13 showing the parts in a different operating position;

FIG. 15 is a fragmentary side elevational view of the parts shown in FIGS. 13 and 14 but in a still different operating position;

FIG. 16 is a fragmentary sectional view approximately on the line 16-16 of FIG. 13;

FIG. 17 is a fragmentary side elevational view similar to FIG. 15 showing a further modified embodiment of the invention;

FIG. 18 is a fragmentary sectional view on the line 18-18 of FIG. 19; and

FIG. 2 is a front elevationalview of the'tensioning or stretching mechanism or apparatus of FIG. 1 showing the sheet clamping units in their up positions with their clamps open, ready to receive a metal sheet to be formed; v

FIG. 3 is a view similar to FIG. 2 but showing the sheet clamps in a different position; v

. FIG. 4 is a plan view of the right-hand sheetstretching assembly as viewed in FIG. 3;

FIG. 5 is a sectional view with portions in elevationapproximately on the line 5-5 of FIGS. 4 and 6;

FIG. 6 is a sectional view with parts in'elevation ap- I proximately on the line 6-6. of FIGS. 4 and 5;

FIG. 7 is a view similar to FIG. 6 but .showing theparts in a different operating position;

parts broken away, showing a further modified con-' struction; 1

FIG. 12 is a sectional view approximately on the line 1212 of FIGS. 11 and 13;

FIG. 13 is a fragmentary sectional view approximately on the line 13-13-or FIG. 11;

FIG. 19 is a fragmentary section view on the line l9-19 of FIGS. 17 and 18.

' DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT apparatus 13 is supported on the press bed 10 and a.

member 26 forming a part of the frame 28 of the work stretching unit in turn supports a stationary drawing die 30 having an upwardly facing convex working face for cooperation with the concave face of the movable die 18. The dies 18, 30 are shown in dot-dash lines and define when closed a concave-convex pattern into which sheet metal stock S also shown in dot-dash line is drawn by the dies. The sheet stock is tensioned or stretched bythe tensioning or stretching mechanism B prior to and/or during the forming operation.

The work tensioning and/or stretching assembly B in addition to the frame assembly 28 previously referred to comprises two sheet gripping assemblies C, C adjacent two'opposit'e ends of the member 26 and of the stationary die 30. The sheet gripping assemblies at opposite ends of the stationary die are alike and only the right-hand assembly C as viewed in FIG. 1 will be described in detail. The corresponding parts of the leftconnected to the upper side of a generally horizontal plate 46 forming a part of the stretching mechanism or assembly B and extending to opposite sides of the member 26 supported thereon. The piston elements of mo-.

tors 42, 44 are pivotally connected to a generally horizontal plate 48 of the frame assembly 40 of the shet gripping assembly C.

The sheet clamp or clamping unit D includes lower and upper jaw or clampmembers 50, 52; respectively, extending lengthwise of the right-handend of the stationary die 30, as viewed in FIGS. 1-3 of the drawings.

, The lower clamp member 50 is detachably connected to the upper side of plate 48 and the upper clamp '52 is pivotally connected to lower clamp 50 and is adapted to be rotated about its pivotal connection with the lower clamp 50 to selectively clamp and release a sheet S of material to be formed by a series of double-acting reciprocating type fluid pressure actuated motors 60, the cylinder elements of which are pivotally connected to the upper side of the plate 48 to the outside or righthand side of the lower clamp member and the piston elements of which are connected to the upper ends of levers 62 fixedly secured to the upper pivoted clamp member 50.

The sheet clamp unit D is adapted to be moved lengthwise of the path of relative movement between the movable and stationary dies 16, 30, that is, in the embodiment show-n in a general vertical direction, by the fluid pressure actuated motors 42, 44. The unit C is guided in its vertical movement by parallel motion mechanism including two pairs of link members 70, 72 and 74, 76 at opposite ends of the unit. In the embodiment shown in FIGS, 1-8, the lefthand ends of the link members 70, 72 and 74, 76, as viewed in FIGS. 1-3, are pivotally connected to stationary pivots or pivot pins 80, 82, respectively, connected to the member 26. The opposite ends of the link member are pivotally connected to pivots or pivot pins 90, 92, 94, 96, respectively, connected to members 100, 102. 104, 106, slidably supported in suitable guide slots 110, 112, 114, 116 in end plates 118, 120, depending from opposite ends of plate 48 of the frame 40. The link members are of equal length and the pivots therefor are normally equal distances from the pivot adjacent thereto, thus forming parallelograms or parallel motion mechanisms at opposite ends of the stretching assembly B. The axes of the pin pivots 80 are aligned as are the axis of the pair of pivots 82 and the pairs of pivots 90, 94 and 92, 96. The plates 118 and 120 are fixed to plate 48 as by welding.

The clamp unit, D is adapted to be moved towards and from the side of the stationary die adjacent thereto by double-acting fluid pressure actuated motors 130, 132, the cylinder elements of which are pivotally connected to member 26 and the piston elements of which are pivotally connected to vertical cams or cam members 134, 136.The lower end of cam members 134, 136 are in turn pivotally connected by pivot pins 140, 142 connected to platelike members 152, 154 and 156, 158, respectively, of the frame member 26, for adjustment of the cam members towards and from the lower diel This adjustment is accomplished by inserting the pivot pins in one of a series of pairs of apertures 159 in members 152,154 and 156,158. 156, 158.

The cam members 134, 136 are oriented in a generally vertical direction and each include cam surfaces .160, 162 provided by slots 164 extending lengthwise of the cam members and through which slot pins or cylindrical cam follower members 166, 168 extend. The

members 166, 168 are connected to the lower ends of plate-like members 170, 172 and 174, 176, respectively, fixed to the underside of member 48 and extending downwardly therefrom. The cam surfaces provided by the slots 164 determine the path of travel of the clamp assembly D in its upward movement at the side of the stationary die which path of movement is preferably parallel with the path of relative movement between the forming dies During the downward movement of clamp assembly D a roller 180 rotatably supported in members 182, 184 fixed to the underside of plate 48 of the frame 40 is caused to engage a cam surface 186 on a cam member 188, detachably connected to the left-hand side of frame 26, by the fluid pressure actuated motors 130, 132, which during the downward movement of the clamp assembly D are supplied with fluid under pressure in such a direction that they pull or bias the levers 134, 136 toward the frame 26. Because the contact of the cam follower 180 with the cam surface 186 is intermediate the clamp surfaces of the clamp members 50, 52 and the connection of the lower links 72, 76 with the member 26 and the slide members 102, 106, referring to the direction of movement of the movable die 16, the down movement of the assembly or unit C causes the members 102, 106 to engage the ends of the slots 112, 116 and thus take the reaction or strain incident to tensioning and stretching the work sheet.

During the upward or return movement of clamp assembly D the clamps 50, are open and motors 130, 132 are actuated in the direction to swing cam members 134, 136 to a position where the slots therein are vertical and the clamp assembly moves vertically as the members 166, 168 follow the cam track provided by the slots 164 in the members 134, 136 and does not follow the cam surface 186. After the clamp assemblies D, D have been returned to their up positions and the drawn work sheet S removed from the press, motors 130, 132 are actuated to return the roller into contact with cam surface 186. The path followed by the clamp assembly during one working cycle is shown in dot-dash lines in FIG. 8 and designated by the reference character 190.

The clamp assemblies D, D can be made to follow any desired path of movement by adjusting the cam 188, the members 134, 136 and/or by varying the configurations of the surface of the cam followed by the cam follower 180 and/or the slots 160 in the cam members 134, 136. Suggested alternative cam surfaces 180a, 180b, 1800, and 1802 are shown in FIG. 9. FIG. 10 shows a cam surface 180/' on an integral part 182a of the stationary lower die 30a. As a further alternative cam members 134, 136 can be replaced by a face cam similar to cam 188 and a suitable cam follower on the clamp assembly to produce the desired upward path and the cam follower biased against the cam by a motor similar to either of the motors 130, 136 but connected directly to the clamp assembly or unit D.

A sheet gripping assembly E of different construction from the sheet gripping assemblies C, C shown in FIGS. 1 to 8 but embodying the invention, is shown in FIGS. 11 to 15. Merely the assembly E for location at the righthand end of the stationary die as the press is viewed in FIG. 1 is shown and described. It is to be understood, however, that a similar assembly but of the opposite hand is employed at the opposite end of the die. The principal differences between the sheet gripping assemblies C and'E is that the cam which determines the path of movement of the sheet clamping unit F of assembly. E relative to the stationary die 30 is adjustable for facilitating changing the path of movement of the unit F as it travels from its up to its down position, the fluid pressure motors which move the unit F away from the cam during the up movement of the unit are incorporated in the upper guiding links or link means of the parallel motion mechanism which connect the opposite ends of the unit F to the frame member upon which the die-30is supported, and the pivots,

for the link means are fixed with respectto the unit E and the frame member.

The sheet clamping assembly or unit F comprises a built-up frame assembly 240 supported by two doubleacting reciprocating type fluid motors 242, 244, the cylinder elements of which are pivotally connected to the upper side of a generally horizontal plate 246 forming a part of the frame assembly of the sheet tensioning or stretching mechanism and extending to opposite sides of the lower die 30 supported thereon. The piston elements of motors 242, 244 are pivotally connected to a plate 248 of frame assembly 240. The plate 248 carries lower and upper clamp members 250, 252, respectively, extending lengthwise of the right-hand end of the stationary die 30. The sheet clamps 250, 252 are similar to the clamps 50, 52 except that the upper clamp 252 has an additional operating motor 260.

The sheet clamp or clamping unit F is moved lengthwise of the path of relative movement between the movable and stationary dies by the fluid pressure actuated motors 242, 244. Pairs of links or link assemblies 270, 272 and 274, 276 of fixed and extendible lengths at opposite ends of the sheet clamp unit F have their one ends connected by pivots or pivot pins 280, 282, respectively, to frame member 226 and their opposite ends connected to pivot pins 290, 292, 294, 296, respectively, fixedly connected to plates 318, 320 of frame 240. The link assemblies 270, 272, and 274, 275 etc., can be considered a parallel motion mechanism as the pivots for the assemblies at opposite ends of the stretching assembly E form parallelograms which are duplicates of one another.

During downward movement of the gripping assembly F a pair of rollers 300, 302 rotatably supported on a shaft 304 carried in the frame 240 engage a cam surface 306 on a cam member 308, the upper end of which is pivotally supported on aligned cylindrical members 310, 312 pivotally carried by the frame member 226 which supports the lower stationary die 30. The lower end of the cam 308 is pivotally connected by similar cylindrical members 314, 316 carried by members 320, 322. The members 320, 322 are connected to the lefthand ends of threaded members 324, 326 which are rotatable relative thereto. The opposite ends of the threaded members engage nut members 330, 332 which are pivotally connected by cylindrical members 334, 336 and 338, 340 carried by members 342, 344 forming a part of the frame 226. The threaded members 336, 338 are rotated within the nut members 330, 332, respectively, upon manual rotation of a shaft 350 connected thereto by pairs of miter gears 352, 354. The shaft 350 extends transversely of the die 30 .with an end projecting to one side of the frame 226 where it is provided with a crank 356 for manual rotation of the same and adjustment of the lower part of the cam 308 towards and from the adjacent side of the stationary die.

The ends of the shaft 304 are in effect cam followers 360, 362 adapted to engage vertically orientated cam tracks 370, 372 on cam members 374, 376 having their lower end pivotally connected to the lower part of the cam member 308 for adjustment relative thereto by bolts 390, 382. the heads of which are pivotally connected to the cam member 308 above the pivotal connection of the cam members 374, 376 thereto. The cam members 374, 376 are preferably adjusted by the bolts 380, 382 so that the cam surfaces 370, 372 thereof are generally lengthwise of the path of relative movement between the die members and the construction of the cam surfaces 306 and 370, 372 is preferably such that when the clamping unit F is in its down position shown in FIG. 14 there is little if any clearance between the cam and cam followers. There will be clearance at most if not all other times as the lower clamp follows a closed path 385 as indicated in dot-dash lines in FIG. 15, the up or return travel of which is or is substantially parallel with the path of relative movement between the forming dies.

During the downward movement of the sheet gripping unit the rollers 300, 302 are held in engagement with the cam surface 306 by the tension in the work sheet. Before initiation of the up or return movement of the clamping assembly F the sheet gripping clamps 250, 252 are opened. During return of the sheet clamping assembly F to its up position the ends of the shaft 304 which are in effect cam followers are held in engagement with the cam surfaces 370, 372 by fluid pressure actuated motors 390, 392 incorporated in the upper links or link assemblies 270, 274. After the sheet clamping unit F has returned to its up position and the formed sheet removed the direction of flow fluid to the motors 390, 392 is reversed returning the cam followers 300, 302 into engagement with the cam surface 306 and in position for reloading. The lower link assemblies 272 and 276 are below the working part of the cam surface 306, that is, the part thereof engaged by the cam followers 300, 302 with the result that the upper link assemblies 270,274 270, 274 not under stress incident to the stretching of the metal sheet being worked. The stress is on the cam and cam followers and the lower link assemblies.

The sheet claimping unit F may be caused to follow different paths from that shown as it travels from and returns to its loading position by adjusting the cam members 308 and/or 374 and 376 or by substituting for the cam members shown members having different suitable cam surface configurations as has been previously suggested.

Since the principal functions of the upper link assemblies 270,274 are to bias or hold the cam followers formed by the end of the shaft 304 against the cam surfaces 370, 375 during the up part of the working cycle and to move the clamping or gripping assembly F into loading position after the formed sheet has been removed from the press and hold it there until a new work sheet has been loaded and the ends thereof clamped in the assemblies F at opposite ends of the stationary die the upper link assemblies may be omitted and other means employed to move the clamping assemblies towards and from the stationary die adjacent thereto as illustrated in FIGS. 17 to 19. The parts of the tensioning and/or stretching mechanism H shown in FIGS. 17 to 19 which are duplicates of the parts employed in the similar mechanism E of the embodiment shown in FIGS. 1 1 to 16 are designated by the same reference character with a prime mark affixed or added thereto and will not be described in detail.

The tensioning and/or stretching mechanism H shown in FIGS. 17 to 19 is similar to that shown in FIGS. 11 to 16 except for the omission of the upper link assemblies and the employment of a reciprocating type, double action, fluid pressure actuated motor K located intermediate the sides of the clamping unit and the end of the stationary die supporting member 26 adjacent thereto to bias and move the grip unit L from and towards the end of the stationary die adjacent thereto. As shown, the piston element 400 of the motor K is pivotally or rotatably connected to the shaft 304 and the cylinder element 402 to a plate 404 of the frame 226 through a bracket 406. In order to accommodate the motor K the cam 308 and the end plate 408 of the frame 226 are provided with suitable openings therein. As previously mentioned various devices other than the motor K could be used to move the clamp unit towards or form the lower die.

A sheet tensioning and stretching mechanism I-I similar to that shown in FIGS. 11 to 16 but of further modified construction is shown in FIGS. 17 to 18. Merely the sheet gripping assembly K employed in stretching mechanism H at the right-hand end of the stationary die as the press is viewed in FIG. 1 is shown and herein described. The stretching mechanism H as does the mechanism B of the embodiment shown in FIGS. 1 to 8, includes a second similar sheet gripping at the other end of the stationary die.

Prior mechanical link systems used in stretch-draw metal forming presses were limited to use with dies having certain configurations because the path of the gripper jaws during the stretch-draw forming operation was fixed. Loading and unloading of the presses preferably takes place at the same station. This is particularly so when mechanical loading and unloading mechanism is employed. Because of this the prior mechanical link systems have the further disadvantage of distorting the formed metal plate or panel, elongated in the forming operation, because of the return of the gripping jaws to the loading and unloading station along the same path as that travelled during the forming operation. The present invention utilizing individual cams which are or may be adjustable for determining the path or paths of movement of the gripping jaws during their forming and return movements and thus provides for movement of the gripping jaws in the proper forming path to produce the exact elongation required of the work sheet for various die configurations and return of the gripping jaws along a second or different path which path is preferably vertical or parallel to the path of relative die movement. This prevents distortion of the formed sheet or panel as it is returned to the unloading and loading station.

From the foregoing description of the preferred embodiments of the invention it will be apparent that the objections heretofore enumerated and others have been accomplished and that there has been provided stretch-draw metal forming apparatus which in addition to being relatively inexpensive to manufacture and easy to maintain in service has many other advantages, some of which have been heretofore referred to.

While preferred embodiments of the invention have been shown and described in considerable detail the invention is not limited to the construction shown and it is intended to hereby cover all adaptations, modifications and uses thereof which come within the practice of those skilled in the art to which the invention pertains and the scope of the appended claims.

I claim:

1. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a die having a nonplanar work face, means supporting said clamping units for movement in opposite directions relative to the die transversely of the work face of the die and at least one of said clamping units lengthwise of the work face of the die, and means causing at least one of said clamping units to follow a predetermined path lengthwise of the work face of the die in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction transversely of the working face of the die and further causing at least one of said clamping units to follow a different path lengthwise of the working face of the die without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.

2. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a die having a nonplanar work face, means supporting said clamping units for movement in opposite directions relative to the die transversely of the work face of the die and at least one of said clamping units lenghtwise of the work face of the die, means causing at least one of said clamping units to follow a predetermined path lengthwise of the work face of the die in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction transversely of the working face of the die, and cam means causing at least one of said clamping units to follow a different path lengthwise of the working face of the die without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.

3. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies movable relative to one another in a predetermined path and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite directions relative to the drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, and means causing at least one of said clamping units to follow a predetermined path cross wise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between the drawing dies and further causing at least one of said clamping units to follow a path crosswise of the path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.

4. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies movable relative to one another in a predetermined path and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite directions relative to the drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between the drawing dies, and cam means causing at least one of said clamping units to follow path crosswise of the path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping unit in the direction opposite to said one direction.

5. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies movable relative to one another in a predetermined path and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite direction relative tov the drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, and cam means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between the drawing dies and further causing at least one of said clamping units to follow a path crosswise of the path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping unit in the direction opposite to said one direction.

6. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies movable relative to one another in a predetermined path and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite directions relative to the drawing dies in opposite directions generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, and means causing at least one of said clamping units to move crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units lengthwise of the path of relative movement between the drawing dies and generally parallel to the path of relative movement between the drawing dies during movement of said clamping units in the direction opposite to said one direction.

7. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite directions relative to the drawing dies in opposite directions generally lengthwise of the path of relative movement between "the drawing dies and at least one of said clamping units drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between the drawing dies, and cam means causing said one of said clamping units to move generally parallel to the path of relative movement between the drawing dies during movementof said clamping units in the direction opposite to said one direction.

8. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies in opposite directions generally lengthwise of the path of relative movment between the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of saidpath of relative movement between said drawing dies, and means causing at least one of said clamping units to move crosswise of said path of relative movement between said drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units lengthwise of said path of relative movement between said drawing dies in one direction and generally parallel to said path of relative movement between said drawing dies during movement of said clamping units in the direction opposite to said one direction.

9 In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable in opposite direction relative to said drawing'dies generally lengthwise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units crosswise of said path of relative movementbetween said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, and means causing at least one of said clamping units to follow a predetermined path crosswise-of the path of relative movement between the drawing dies in the direction away therefrom to' increase the relative distance between units in one direction lengthwise of said path of relative movement between said drawing dies and further causing at least one of said clamping units to follow a different path crosswise of the path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one di rection without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.

10. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in apredetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies generally lengthwise of the path of relative movement betwen the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relative movement between said drawing dies, and cam means causing at least one of said clamping units to follow a path crosswise of the path of relative movment between the drawing dies different from the path followed during'movement of said clamping units in said one direction without decreasing the relative distance said clamping units during movement of said clamping units in the direction opposite to said one direction.

11. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of the path of relative movement between said drawing dies, and cam means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between said drawing dies and a path crosswise of path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.

12. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one naother in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, and means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relative movement between said drawing dies and parallel to said path of relative movement between said drawing dies during movement of said clamping units in the direction opposite to said one direction.

13. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relative movement between said drawing dies, and cam means causing said one of said clamping units to travel generally parallel to said path of relative movement between said drawing dies during movement thereof in the direction opposite to said one direction.

14. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said dies and movable relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, and cam means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relative movement between said drawing dies and generally parallel said path of relative movement between said drawing dies during movement of said clamping units in the direction opposite to said one direction.

15. In a stretch unit for a draw die forming press, a frame assembly adapted to support a drawing die, work clamping units adjacent to opposite ends of said frame assembly and supported by said frame assembly for movement relative thereto by means including double acting reciprocating type fluid pressure actuated motors pivoted to said frame assembly, cam means including cam and cam follower elements adjacent said opposite ends of said frame assembly, one being operatively connected to said frame assembly and the other to said clamping units, cam members providing vertically oriented cams pivotally connected to said frame assembly adjacent said opposite ends, cam follower members on said clamping units engageable with said cams, and double-acting reciprocating type fluid pressure actuated motors connected to said frame assembly and to said cam members for moving said cam members about their pivotal connections with said frame assembly.

16. In a stretch unit for a draw die forming press, a frame assembly adapted to support a drawing die, work clamping units adjacent to opposite ends of said frame assembly and supported by said frame assembly for movement relative thereto by double-acting reciprocating type fluid pressure actuated motors pivoted to said frame assembly and parallel motion mechanism including-vertically spaced generally horizontal parallel link means pivotally connected to said frame assembly and to said clamping units, cam means including cam and cam follower elements adjacent said opposite ends of said frame assembly, one being operatively connected to saidframe assembly and the other to said clamping units, cam members providing vertically oriented cam surfaces pivotally connected to said frame assembly adjacent said opposite ends, cam follower members on said clamping units engaged with said cam surfaces on said cam members and double-acting reciprocating type fluid pressure actuated motors connected to said frame assembly and to said cam members for moving said cam members about their pivotal connections with said frame assembly, the pivotal connection of said links means with one of said frame assembly or said clamping units being movable.

17. In a draw die forming press, a frame assembly adapted to support a lower stationary drawingdie and an upper reciprocable drawing die, means for reciprocating said upper drawing die towards and from said stationary die, work clamping units adjacent to opposite ends of said stationary die and supported by said frame assembly for movement relative thereto by double-acting reciprocating type fluid pressure actuated means, and'links having their opposite ends pivotallyconnected to said frameassembly and to said clamping units, the pivots to which one end of each of said links is connected being movable relative to said frame assembly or to said clamping unit to which it isconnected.

18. In a stretch unit for a draw die forming press, a frame assembly comprising a support for a drawing die having a nonplanar work face, work clamping units, reciprocating type fluid pressure actuated motors and parallel motion mechanism including upper and lower generally horizontal parallel link means pivotally con.- nected to said frame assembly and to said clamping units and supporting said clamping unitsfor movement assembly, reciprocating type fluid pressure actuated motors and parallel motion mechanism including upper and lower generally horizontal parallel link means pivotally connected to said frame assembly and to said clamping units supporting said units for movement relative to said frame assembly, each of said upper link means comprising a reciprocating type fluid pressure actuate d motor including piston and cylinder elements' one connected to said frame assembly and the other to said clamping units, vertically orientated cooperative cam means adjacent said opposite ends of said frame assembly operatively connected to said frame assembly and to said clamping units, and means for actuating said reciprocating type fluid pressure actuated motors for moving said cooperating cam means into and out of.

-vertical direction, vertically orientated cooperating sembly and to'said clamping units formoving said clamping units and in turn said cam means into and out cam means adjacentsaidopposite ends of said frame assembly operatively connected to said frame assembly and to said clamping units, and reciprocating type fluid pressure actuated motors connected to'said frameasof engagement.

21. In a stretch unit for a draw dieforming press, a

stretching units and pivoted to 'said frame assembly,

generally horizontal link means pivotally connected to said frame assembly and to saidwork stretching units, said work stretching units having sheet clamping means a spaced from said link means in the direction of the path' .of relative movement between the drawing dies, cam

means intermediate said link means and saidsheet clamping means operatively connected to said frame assembly and to said work-stretching units for moving relative to said frame assembly in opposite directions both lengthwise and transversely of the work face'of a drawing die on said die support, each of said upper link means comprising a reciprocating type fluid pressure versely of the work face of the die when moved in opposite directions.

19. In a stretch unit for a draw die forming press, a frame assembly adapted to support a drawing die, work clamping units adjacent to opposite ends of saidframe said sheetclamping means in a predetermined path 1 crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units upon movement of said work stretching units in one'direction generally lengthwise of the path of relaconnected to said frame assembly and to said work stretching units for selectively moving said work stretching units relative to said frame assembly transversely of the path of relative movement between the drawing dies.

22. In a stretch unit for a draw die forming press, a

frame assembly adapted to support one of two drawing dies, work stretching units adjacent to opposite ends of said frame assembly supported for movement generally lengthwise of the path of relative movement between said drawing dies by reciprocating type fluid pressure actuated motors connected thereto and pivoted to said frame assembly and generally horizontal link means pivotally connected to said frame assembly and to said stretching units adjacent to one of their ends in the direction of the path of relative movement between the drawing dies, said stretching units having sheet clamping means adjacent to their other ends in the direction of the path of relative movement between the drawing dies, first cam means intermediate said link means and said clamping means operatively connected to said frame assembly and to said stretching units for moving said clamping means in a predetermined path upon movement of said stretch units in one direction generally lengthwise of the path of relative movement bemovement between the drawing dies. 

1. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a die having a nonplanar work face, means supporting said clamping units for movement in opposite directions relative to the die transversely of the work face of the die and at least one of said clamping units lengthwise of the work face of the die, and means causing at least one of said clamping units to follow a predetermined path lengthwise of the work face of the die in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction transversely of the working face of the die and further causing at least one of said clamping units to follow a different path lengthwise of the working face of the die without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.
 2. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a die having a nonplanar work face, means supporting said clamping units for movement in opposite directions relative to the die transversely of the work face of the die and at least one of said clamping units lenghtwise of the work face of the die, means causing at least one of said clamping units to follow a predetermined path lengthwise of the work face of the die in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction transversely of the working face of the die, and cam means causing at least one of said clamping units to follow a different path lengthwise of the working face of the die without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.
 3. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies movable relative to one another in a predetermined path and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite directions relative to the drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, and means causing at least one of said clamping units to follow a predetermined path cross wise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between the drawing dies and further causing at least one of said clamping units to follow a path crosswise of the path of relative movement between the drawing dies different from the path followed during Movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.
 4. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies movable relative to one another in a predetermined path and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite directions relative to the drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between the drawing dies, and cam means causing at least one of said clamping units to follow path crosswise of the path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping unit in the direction opposite to said one direction.
 5. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies movable relative to one another in a predetermined path and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite direction relative to the drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, and cam means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between the drawing dies and further causing at least one of said clamping units to follow a path crosswise of the path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping unit in the direction opposite to said one direction.
 6. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies movable relative to one another in a predetermined path and having opposed nonplanar work faces, means supporting said clamping units for movement in opposite directions relative to the drawing dies in opposite directions generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, and means causing at least one of said clamping units to move crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units lengthwise of the path of relative movement between the drawing dies and generally parallel to the path of relative movement between the drawing dies during movement of said clamping units in the direction opposite to said one direction.
 7. In apparatus for stretch-drawing a metal sheet, work clamping units for location adjacent to opposite ends of a pair of drawing dies and having opposed nonplanar work faces, Means supporting said clamping units for movement in opposite directions relative to the drawing dies in opposite directions generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between the drawing dies, means for moving said clamping units generally lengthwise of the path of relative movement between the drawing dies, means causing at least one of said clamping units to move crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between the drawing dies, and cam means causing said one of said clamping units to move generally parallel to the path of relative movement between the drawing dies during movement of said clamping units in the direction opposite to said one direction.
 8. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies in opposite directions generally lengthwise of the path of relative movment between the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, and means causing at least one of said clamping units to move crosswise of said path of relative movement between said drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units lengthwise of said path of relative movement between said drawing dies in one direction and generally parallel to said path of relative movement between said drawing dies during movement of said clamping units in the direction opposite to said one direction.
 9. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable in opposite direction relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, and means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relative movement between said drawing dies and further causing at least one of said clamping units to follow a different path crosswise of the path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.
 10. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies generally lengthwise of the path of relative movement betwen the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relativE movement between said drawing dies, means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relative movement between said drawing dies, and cam means causing at least one of said clamping units to follow a path crosswise of the path of relative movment between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance said clamping units during movement of said clamping units in the direction opposite to said one direction.
 11. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of the path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of the path of relative movement between said drawing dies, and cam means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of the path of relative movement between said drawing dies and a path crosswise of path of relative movement between the drawing dies different from the path followed during movement of said clamping units in said one direction without decreasing the relative distance between said clamping units during movement of said clamping units in the direction opposite to said one direction.
 12. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one naother in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, and means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relative movement between said drawing dies and parallel to said path of relative movement between said drawing dies during movement of said clamping units in the direction opposite to said one direction.
 13. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said drawing dies and movable relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relaTive movement between said drawing dies, and cam means causing said one of said clamping units to travel generally parallel to said path of relative movement between said drawing dies during movement thereof in the direction opposite to said one direction.
 14. In apparatus for stretch-drawing a metal sheet, a pair of drawing dies movable relative to one another in a predetermined path, work clamping units adjacent to opposite ends of said dies and movable relative to said drawing dies generally lengthwise of the path of relative movement between the drawing dies and at least one of said clamping units generally crosswise of said path of relative movement between said drawing dies, means for moving said clamping units generally lengthwise of said path of relative movement between said drawing dies, and cam means causing at least one of said clamping units to follow a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units during movement of said clamping units in one direction lengthwise of said path of relative movement between said drawing dies and generally parallel said path of relative movement between said drawing dies during movement of said clamping units in the direction opposite to said one direction.
 15. In a stretch unit for a draw die forming press, a frame assembly adapted to support a drawing die, work clamping units adjacent to opposite ends of said frame assembly and supported by said frame assembly for movement relative thereto by means including double acting reciprocating type fluid pressure actuated motors pivoted to said frame assembly, cam means including cam and cam follower elements adjacent said opposite ends of said frame assembly, one being operatively connected to said frame assembly and the other to said clamping units, cam members providing vertically oriented cams pivotally connected to said frame assembly adjacent said opposite ends, cam follower members on said clamping units engageable with said cams, and double-acting reciprocating type fluid pressure actuated motors connected to said frame assembly and to said cam members for moving said cam members about their pivotal connections with said frame assembly.
 16. In a stretch unit for a draw die forming press, a frame assembly adapted to support a drawing die, work clamping units adjacent to opposite ends of said frame assembly and supported by said frame assembly for movement relative thereto by double-acting reciprocating type fluid pressure actuated motors pivoted to said frame assembly and parallel motion mechanism including vertically spaced generally horizontal parallel link means pivotally connected to said frame assembly and to said clamping units, cam means including cam and cam follower elements adjacent said opposite ends of said frame assembly, one being operatively connected to said frame assembly and the other to said clamping units, cam members providing vertically oriented cam surfaces pivotally connected to said frame assembly adjacent said opposite ends, cam follower members on said clamping units engaged with said cam surfaces on said cam members and double-acting reciprocating type fluid pressure actuated motors connected to said frame assembly and to said cam members for moving said cam members about their pivotal connections with said frame assembly, the pivotal connection of said links means with one of said frame assembly or said clamping units being movable.
 17. In a draw die forming press, a frame assembly adapted to support a lower stationary drawing die and an upper reciprocable drawing die, means for reciprocating said upper drawing die towards and from said stationary die, work clamping units adjacent to opposite ends of said stationary die and supported by said frame assembly for movement relative thereto by double-acting reciprocating type fluid pressure actuated motors pivoted to said frame assembly, stationary cam meaNs adjacent said opposite ends of said stationary die and facing in opposite directions, cam followers on said clamping units engageable with said cam means, cam members pivotally connected to said frame assembly adjacent said opposite ends of said stationary die and providing vertically oriented cam surfaces, members on said clamping units engaged with said cam members, double-acting reciprocating type fluid pressure actuated motors connected to said frame assembly and to said cam members for moving said clamping units and in turn said cam followers towards and from said cam means, and links having their opposite ends pivotally connected to said frame assembly and to said clamping units, the pivots to which one end of each of said links is connected being movable relative to said frame assembly or to said clamping unit to which it is connected.
 18. In a stretch unit for a draw die forming press, a frame assembly comprising a support for a drawing die having a nonplanar work face, work clamping units, reciprocating type fluid pressure actuated motors and parallel motion mechanism including upper and lower generally horizontal parallel link means pivotally connected to said frame assembly and to said clamping units and supporting said clamping units for movement relative to said frame assembly in opposite directions both lengthwise and transversely of the work face of a drawing die on said die support, each of said upper link means comprising a reciprocating type fluid pressure actuated motor including piston and cylinder elements one connected to said frame assembly and the other to said clamping units for lengthening said upper links during movement of said clamping units in one direction transversely of the work face of the die to cause said clamping units to follow different paths transversely of the work face of the die when moved in opposite directions.
 19. In a stretch unit for a draw die forming press, a frame assembly adapted to support a drawing die, work clamping units adjacent to opposite ends of said frame assembly, reciprocating type fluid pressure actuated motors and parallel motion mechanism including upper and lower generally horizontal parallel link means pivotally connected to said frame assembly and to said clamping units supporting said units for movement relative to said frame assembly, each of said upper link means comprising a reciprocating type fluid pressure actuated motor including piston and cylinder elements one connected to said frame assembly and the other to said clamping units, vertically orientated cooperative cam means adjacent said opposite ends of said frame assembly operatively connected to said frame assembly and to said clamping units, and means for actuating said reciprocating type fluid pressure actuated motors for moving said cooperating cam means into and out of engagement.
 20. In a stretch unit for a draw die forming press, a frame assembly adapted to support a drawing die, work clamping units adjacent to opposite ends of said frame assembly, reciprocating type fluid pressure actuated motors and generally horizontal link means pivotally connected to said frame assembly and to said clamping units supporting said units for movement in generally vertical direction, vertically orientated cooperating cam means adjacent said opposite ends of said frame assembly operatively connected to said frame assembly and to said clamping units, and reciprocating type fluid pressure actuated motors connected to said frame assembly and to said clamping units for moving said clamping units and in turn said cam means into and out of engagement.
 21. In a stretch unit for a draw die forming press, a frame assembly comprising a die support for one of two drawing dies movable relative to one another in a predetermined linear path, work stretching units adjacent to opposite ends of said die support, reciprocating type fluid pressure actuated motors connected to said work stretching units and pivoted to said frame assembly, generally horizoNtal link means pivotally connected to said frame assembly and to said work stretching units, said work stretching units having sheet clamping means spaced from said link means in the direction of the path of relative movement between the drawing dies, cam means intermediate said link means and said sheet clamping means operatively connected to said frame assembly and to said work stretching units for moving said sheet clamping means in a predetermined path crosswise of the path of relative movement between the drawing dies in the direction away therefrom to increase the relative distance between said clamping units upon movement of said work stretching units in one direction generally lengthwise of the path of relative movement between the drawing dies, and reciprocating type fluid pressure operated motors operatively connected to said frame assembly and to said work stretching units for selectively moving said work stretching units relative to said frame assembly transversely of the path of relative movement between the drawing dies.
 22. In a stretch unit for a draw die forming press, a frame assembly adapted to support one of two drawing dies, work stretching units adjacent to opposite ends of said frame assembly supported for movement generally lengthwise of the path of relative movement between said drawing dies by reciprocating type fluid pressure actuated motors connected thereto and pivoted to said frame assembly and generally horizontal link means pivotally connected to said frame assembly and to said stretching units adjacent to one of their ends in the direction of the path of relative movement between the drawing dies, said stretching units having sheet clamping means adjacent to their other ends in the direction of the path of relative movement between the drawing dies, first cam means intermediate said link means and said clamping means operatively connected to said frame assembly and to said stretching units for moving said clamping means in a predetermined path upon movement of said stretch units in one direction generally lengthwise of the path of relative movement between the drawing dies, second cam means operatively connected to said frame assembly and to said stretching units for moving said clamping means in a different path upon movement of said stretching units generally lengthwise of the path of movement between the drawing dies in the opposite direction, and reciprocating type fluid pressure operated motors operatively connected to said frame assembly and to said stretching units for moving said stretching units relative to said frame assembly transversely of the path of relative movement between the drawing dies. 